Voltage standing wave ratio detecting and adjusting apparatus

ABSTRACT

Hysteresis type detection apparatus for detecting the voltage standing wave ratio (VSWR) of a transmitting system. When the detection apparatus determines that the VSWR exceeds a predetermined value, it actuates a servo-system which adjusts impedances in a coupling unit between the transmitter and the antenna and continues the adjustment until the VSWR is at a value substantially lower than it was upon initial actuation of the servo-apparatus.

1 021. a. a f IPE/102 XR 398429358 Q i I M Umted States P, ,s42,35s

m Frazier 1 ()Ct. 15, 1974 4 [54] VOLTAGE STANDING WAVE RATIO "fi st3,614,466 /1971 Grundy 1. 322 140 X DETECTING AND ADJUSTING APPARATUS3,659,210 4/1972 Nllsson 328/140 X 3,717,8l8 2/1973 Herbst 307/233 XInventor: Melvin Frazier, Manon, Iowa 3,783,394 1/1974 Avery 307/233 x[73] Assignee: Collins Radio Company, Dallas,

Prtmary Examiner-Alfred L. Brody Attorney, Agent, or FirmBruce C. Lutz[22] Filed: June 18, 1973 [21] Appl. No.: 371,099 [57] ABSTRACTHysteresis type detection apparatus for detecting the 52 us. (:1329/129, 307/233, 328/140, voltage Standing wave ratio of n transmitting329/103" 330/30 D system. When the detection apparatus determines that51 1m. (:1. 1103a 3/10 the VSWR exceeds a predetermined value, itacwntes 58] Field of Search 329/103, 129, a Servo-System which adjustsimpedanc'es in a Coupling 32 141 33; 307 233; 330 3 D unit between thetransmitter and the antenna and continues the adjustment until the VSWRis at a value [56] 9 References Cited substantially lower than it wasupon initial actuation of UNITED STATES PATENTS the P 3,541,457 11 1970Leighty et al...; 329/129 ux 3 Claim 10 Drawing Figures FWD PovygR PKIO1 2 REF'L P QlNER 22 24 Z 3&142231343 OR 1h? 329 /12? PATENIEU 3.842358SHEET 10? 9 FWD POWER r0 [2 i l 28 30 32 REF'L P WER 22 2 4 TUNING T FNETWORK TRANSCEIVER I f (COUPLER) I i 82 as 76 80 75 1 I 1 I PHASINGIMPEDANCE FORWARD REFLECTED DISC DISC POWER POWER 84R r VSWR. sERvOsERvO RATIO 7 DETECTOR -FIG. 2

VOILTAGE STANDING WAVE RATIO DETECTING AND ADJUSTING APPARATUS Thepresent invention is directed generally to elecl tronics and morespecifically to a signal transmitting system using an antenna.

In most signal transmission systems using a radiating type antenna thepower is applied to the antenna at a reduced level until the VSWR isadjusted to less than a prescribed value. At this point, the power isincreased substantially. Some units incorporate a time delay whichcontinues driving the adjustment apparatus in the same direction for aprescribed time after the VSWR is reduced below the prescribed amount tohopefully result in an even lower VSWR at the end of the prescribedtime. When the higher power output is provided, the reflected powerdetector still operates on providing an indication for the same absolutevalue of reflected power. Thus, if the additional'time provided was notsufficient to drive the VSWR to a value such that the absolute value ofthe reflected power at the new forward power level exceeds theprescribed amount, the device will still notbe operating satisfactorily.

The present invention uses a ratio detecting apparatus so that theactual ratio of reflected power to forward power is detected and thusthe device doesnot need to rely on an experimentally determinedtimedelayed adjustment. Rather, if the VSWR is less than the prescribedamount at the low power transmission level the ratio detector will stillprovide the same indication at the higher level assuming that powerlevels have no effect on the ratio.

' It is therefore an object of the present invention to provide animproved VSWR detection circuit.

A further object of the present invention is to provide improved VSWRdetection and adjustment apparatus for a transmission system.

Further objects and advantages of the present inventive concept may beascertained from a reading of the specification and appendedclaims inconjunction with the drawings wherein:

FIG. 1 is a schematic diagram of one embodiment of a hysteresis typeratio detector;

FIG. 2 is a block diagram of an overall transmission system includingcoupling phase and impedance detection and adjustment means and furtherforward and reflected power detection means in combination with a ratiodetector for actuating the servo-adjustment means when the transmissionsystem is unbalanced by more than a predetermined amount;

FIGS. 3l0 provide detailed schematic diagram illustrations of variousblocks of FIG. 2.

In FIG. I an input terminal supplies a forward power signal indicationthrough a resistor 12 to a first input means 14 of an operational ordifferential amplifier generally designated as 16. Amplifier 16 haspositive and negative power terminal means 18 and 20. respectively. Areflected power input terminal 22 is connected through a resistor 24 toa second input 26 of amplifier I6. An output 28 of amplifier 16 isconnected through a resistor 30 to an apparatus output terminal 32.Apparatus output terminal 32 is connected through a zener diode 34 toground or reference potential 36 for the purpose of preventing theoutput from exceeding a predetermined value as set by the zener diode34. Output terminal 28 is also connected through a first renal 26. Ajunction point between resistors 38 and 40 is connected through aresistor 42 to ground 36. A further zener diode 44 is connected frominput 26 of amplifier 16 to ground 36. A FET transistor generallydesignated as 46 has its source connected to ground 36 and its drainconnected through a resistor 48 to input terminal 26 of amplifier 16. Agate of transistor 46 is connected through a resistor 50 to ground 36and is also connected through series connection of a diode 52 and aresistor 54 to output 28 of amplifier 16.

The operation of FIG. 1 is relatively easy to understand and for initialexplanation purposes the circuit including the FET can be ignored. Ifthe signal appearing at input 14 as passed through resistor 12 is lessthan 1 the signal appearing at 26 as passed through resistor 24,

the output will be at a positive level. Although the signals atterminals 10 and 22 may be different absolute values when the outputfrom amplifier 16 is zero, the resistors 12, 24 and 48 in combinationwith FET 46 adjust these signals so that the output at 28 will beapproximately zero when 14 and26 are equipotential. However, anoperational amplifier with input signals applied thereto is an unstabledevice and acts like a switch due to the high gain therethrough incombination with the feedback and thus the output at 28 would only be ata zero condition for a substantially instantaneous time.

When the signal appearing at input 26 is only minutely less than theforward power signal as appears at input 14, the amplifier 26 willsuddenly switch so that the output which was previously at a largepositive value will become suddenly at a large negative value. Thischange in output signal may be fed to the output 32 and is also suppliedback through the feedback net work comprising resistors 38, 40 and 42 toreinforce this action at input 26.

The negative signal at output 28 had previously kept the FET in an ONcondition. With FET 46 in an ON condition part of the signal appearingat input terminal 22 is shunted to ground. In other words, the inputsignal is divided so that only a partial effect of the voltage appliedat 22 actually appears at 26. With FET 46 turned OFF due to the positivegoing condition of the output signal, the entire voltage appearing atinput 22 is supplied to input 26 of amplifier 16. By this action thesignals appearing at 22 have a much greater effect on the input ofamplifier. Thus, the reflected power signal will have to drop to a muchlower value than was necessary to initially switch the amplifier beforethe effect at 26 produces a voltage which is lower than that appearingat input 14. When this does occur, however, the amplifier will againswitch so that the output is negative and transistor 46 is again switchto an ON condition. Thus, the input signal at 26 is again drasticallylowered and the device will remain in this condition until the ratio ofthe power signals appearing at 10 and 22 are again altered to providethe same conditions as produced the initial switching action.

In view of the above, it may be determined that the device of FIG. 1 hasa hysteresis effect in that it will switch the output signal when agiven ratio occurs but will remain in that condition until a muchdifferent and much lower ratio is obtained. This hysteresis effect isproduced by the circuitry utilizing the F ET 46.

BLOCK DIAGRAM SYSTEM OF FIG. 2

In FIG. 2 an antenna 70 is connected to an output of a tuning network.hereinafter called a coupler 72, which has signals supplied therethroughby a transceiver or other signal transmitting device 74 on a lead 75. Aforward power discriminator 76 is coupled to lead 75 for receivingsignals from the transceiver 74 and to supply an output indicative ofthe forward power detected signal to one input of a VSWR ratio detector78. A reflected power discriminator 80 also detects signals on lead 75as obtained from transceiver 74 and supplies outputs indicative thereofto the detector 78. A phase discriminator 82 is coupled to lead 75 toreceive voltage and current signals from transceiver 74 and providesthese signals to operate a servomechanism 84 which operates anadjustment within coupler 72 to vary the transformation impedancetherein and thus, the phase of signals therein. An impedancediscriminator 86 is coupled to lead 75 and thus. to the transceiver 74to also receive voltage and current indications and thereby determineimpedance. The impedance discriminator 86 provides an operating signalto a servo-mechanism 88 which is mechanically connected to coupler 72 toprovide additional adjustments over and above those provided by servo84. Each of the servos 84 and 88 are connected to an output of detector78 which provides actuation signals so that the servos 84 and 88 mayoperate.

In operation the transceiver 74 initially supplies a low power signalthrough the coupler 72 to antenna 70. This low power preliminaryoperation is used as a time when the coupler is adjusted to obtainmaximum efficiency from the transmitting system. The formula forobtaining VSWR is as follows:

Reflected Power Forward Power I {Reflected Power Forward Power VSWR aspreviously indicated is the voltage standing wave ratio. It is desirablethat this ratio be as low as possible and this is accomplished by makingthe reflected power a minimum value. Such minimum value of the reflectedpower is theoretically obtained by adjusting impedance ratios in thecoupler so that the impedance of the antenna as seen through the couplerby the transmitter is the same as the output impedance of thetransmitter. This impedance will have both inductive and capacitivecomponents.

It is undesirable to continuously alter the impedance of the couplersince this causes unnecessary reduction in the life of the equipment.Thus, adjustment systems are designed such that an adjustment iseffected only when the VSWR exceeds a predetermined amount. It isdesirable to reduce the VSWR to a value far below the value at which theadjustment occurs so that further adjustment will not be needed for sometime. Thus, the detectors 76 and 80 supply input signals to ratiodetector 78 which provides an output to the servos 84 and 88 to actuatethese servos when the ratio of the reflected power to forward powerreaches or exceeds certain prescribed limits. The actuation of the servosystems adjusts coils within coupler 72 through the use of the detectioncircuits 82 and 86 until the ratio of reflected to forward power dropsto a new value much VSWR 4 lower than that causing initial actuation. Atthis time the output signal from detector 78 is deleted and the servosystems 84 and 88 are no longer activated.

The circuits shown in FIGS. 3-10 are merely detailed schematicsindicative of one embodiment of the invention. As such, they are notpertinent to the invention other than illustrating one possibleimplementation of the blocks of FIG. 2.

The circuit schematic of FIG. 3 illustrates the coupler 72 of FIG. 2.The lead labeled RF IN is the lead from transceiver 74. This is passedthrough a coil generally designated as 99 which is variable ininductance and in the position of the tap located on the inductor. Asmay be seen from the dashed lines, the two adjustments are availablefrom the servo-mechanism units. These mechanical inputs correspond tothe dash line mechanical outputs of servos 84 and 88 in FIG. 2. As willbe ascertained. the changing of the inductance will change the phase ofthe signal being transmitted through the coupler and the change of thetap will change the impedance ratio of the signal coupling between thetransceiver 74 and the antenna 70. A lead at the right side of FIG. 3labeled RF OUT is the lead going to antenna 70. The portion labeled drumswitch S8 is merely illustrative of the connections of the drum switchS8 which is shown in the schematic in the home position. Other positionsare indicative of different operating frequencies and are not pertinentto the present invention, although have been shown for completeness ofillustration.

FIG. 4 includes the circuitry for the forward power detector ordiscriminator 76 and the reflected power detector or discriminator 80.In addition, it illustrates the circuitry for the phasing discriminator82 and the impedance discriminator 86. The outputs from these twocircuits which are labeled forward power discriminator (M) and reflectedpower discriminator (U) are the same as the two input leads to the VSWRdetector 78 of FIG. 2.

FIG. 5 again is not pertinent to the present inventive concept but ismerely shown for completeness as it is a frequency band selectioncircuit for the coupler 72.

FIG. 6 illustrates the VSWR detector 78 of FIG. 2 and illustrates inmore detail the basic concept of FIG. 1. The circuitry of FIG. 6 isbeing illustrated again so as to provide complete information as tointerconnection with other parts of the overall system of FIG. 2.

FIG. 7 again is not pertinent to the invention since it is merely aportion of coupler 72 for controlling in part some of the otheroperations of the coupler 72.

FIG. 8 illustrates additional circuitry cooperating with that of FIGS. 5and 7 in the coupler 72. The input KK in FIG. 8 labeled VSWR is thesignal received from the similarly designated lead of FIG. 6.

FIG. 9 includes two servo preamps as utilized in the input portion ofthe servos 84 and 88. The signal inputs CCC and DDD of FIG. 9 arereceived from correspending outputs in the digital logic circuitry ofFIG. 8 through which the output signals from the VSWR detector 78 pass.These enabling or disabling signals cause the servos 84 and 88 toreposition or refrain from repositioning depending upon the mismatch orVSWR between the transceiver 74 and the antenna 70.

The output servo amplifiers of FIG. 10 operate to drive the tap and coilmotors of FIG. 3.

While I have illustrated a specific embodiment of the inrvention, I donot wish to be limited to only that embodiment shown but rather to theconcept of using a hysteresis type ratio detector in conjunction with at servo controlled signal transmitting coupling system wherein the ratioof the forward power to reflected power is detected rather than theabsolute value of the reflected power.

I claim:

1. Hysteresis type ratio detector apparatus comprising, in combination:

differential amplifier means including first and second input means andoutput means;

first and second apparatus signal input means for supplying two variableamplitude signals the ratio of which is to be compared;

means connecting said first and second apparatus signal input means tothe first and second input means of said amplifier means, respectively;apparatus output means for providing an output signal when the ratio ofsignals supplied by said first and second apparatus input signalsexceeds a first given ratio in one direction of voltage change from areference potential and the output signal continuing until the inputsignals exceed a second given ratio in a direction of voltage changeopposite said one direction;

variable impedance means, including control means, for varying inimpedance in response to a control signal;

means connecting said variable impedance means to said first input meansof said amplifier means for altering applied signal levels to saidamplifier means to change from one given ratio to the other given ratiowhen the impedance of said variable impedance means changes; and

means connecting said output means of said amplifier means to saidapparatus output means and to said control means of said variableimpedance means.

2. Apparatus as claimed in claim 1 wherein:

said variable impedance means includes a field effect transistor inseries with a resistor and is turned OFF when the ratio is exceeded insaid one direction; and

said variable impedance means is voltage sensitive.

3. Apparatus as claimed in claim 1 comprising in addition:

reference potential means;

field effect transistor means and first resistance means comprising apartof said variable impedance means and connected between said firstinput means of said differential amplifier means and said referencepotential means, said field effect transistor means including gatemeans;

diode means and second resistance means connected in series between saidcontrol means of said variable impedance means and said gate means ofsaid field effect transistor;

first Zener diode means connected between said apparatus output meansand said reference potential means for limiting the absolute amplitudeof signals appearing at said apparatus output means; and

second Zener diode means connected between said first input means ofsaid differential amplifier means and said reference potential means forlimiting the absolute amplitude of signals applied to said first inputmeans of said differential amplifier

1. Hysteresis type ratio detector apparatus comprising, in combination:differential amplifier means including first and second input means andoutput means; first and second apparatus signal input means forsupplying two variable amplitude signals the ratio of which is to becompared; means connecting said first and second apparatus signal inputmeans to the first and second input means of said amplifier means,respectively; apparatus output means for providing an output signal whenthe ratio of signals supplied by said first and second apparatus inputsignals exceeds a first given ratio in one direction of voltage changefrom a reference potential and the output signal continuing until theinput signals exceed a second given ratio in a direction of voltagechange opposite said one direction; variable impedance means, includingcontrol means, for varying in impedance in response to a control signal;means connecting said variable impedance means to said first input meansof said amplifier means for altering applied signal levels to saidamplifier means to change from one given ratio to the other given ratiowhen the impedance of said variable impedance means changes; and meansconnecting said output means of said amplifieR means to said apparatusoutput means and to said control means of said variable impedance means.2. Apparatus as claimed in claim 1 wherein: said variable impedancemeans includes a field effect transistor in series with a resistor andis turned OFF when the ratio is exceeded in said one direction; and saidvariable impedance means is voltage sensitive.
 3. Apparatus as claimedin claim 1 comprising in addition: reference potential means; fieldeffect transistor means and first resistance means comprising a part ofsaid variable impedance means and connected between said first inputmeans of said differential amplifier means and said reference potentialmeans, said field effect transistor means including gate means; diodemeans and second resistance means connected in series between saidcontrol means of said variable impedance means and said gate means ofsaid field effect transistor; first Zener diode means connected betweensaid apparatus output means and said reference potential means forlimiting the absolute amplitude of signals appearing at said apparatusoutput means; and second Zener diode means connected between said firstinput means of said differential amplifier means and said referencepotential means for limiting the absolute amplitude of signals appliedto said first input means of said differential amplifier means.